Electric-motor control.



W. O. STRANG. ELECTRIC MOTOR CONTROL. APPLICATION FILED "n.4, 1913.

1,261,644. Patented Apr. 2, 191&

14 6. WITNESSES: INVENTUH ATTOR EY UNITED STATES PATENT OFFICE.-

WALTER C. STIRLING, OF YCNKEBS, YEW YORK, ASSIGNOB TO OTIS EIiEVATOR COMPAN Y,

OF NEW YORK, N. Y., A CORPORATION OF NEW JERSEY.

ELECTRIC-ROTOR CONTROL.

Specification of Letters Patent.

Patented Apr. 2, 1918.

Application fled Apt-114, 1918. Serial No. 758,767.

To all whom it may concern:

Be it known that I, VALTER C. STRANG, a citizen of the United States, residing in Yonkers, in the count of Vestchester and State of New York, ave invented a new and useful Improvement in Electric-Motor Control, of which the following is a specihcation. I

My invention relates to improvements in electric motor controlling systems, and has for an object the provision of a simple and eilicient system of motor control which embodies distinctively novel features of practical merit which mark a decided advance over the prior art. l

A further object of the invention is the provision of improved means for slowing down and stopping an electric motor.

Other objects of the invention will appear hereinafter, the novel combinations of elements being pointed out in the annexed claims.

\Vhilc the invention may be used to advantage with electric motors employed for various power purposes, the same is of particular value when used in connection with an electrically driven elevator .o hoist.

It is well known that for a given motor, the greater the field strength is the less current the armature will lake to produce a given torque. For this reason it is very desirable, particularly in the case of an electric elevator system. to insure a powerful lield both in starting and stopping so as to cut down the armature current to a minimum thereby not. only economi'zing current, but reducing the heating of the moi or and the tendency for sparking at the motor brushes. In stopping the motor, it is almost the universal practice to utilize the current generated by the motor to effect a dvnamic brake action, the field of the motor being excited from the main line or from the motor itself, acting as a self-exciting dynamo. This last named method is the one most encrally in use, since it economizes cur rent, at at the same time, it has its disadvantages in that the dynamic brake current is heavy and the field strength rapidly falls off as the speed of the motor is reduced. My invention makes it possible and desirable mse a plain shunt wound motor whose field strength not only does not fall off with reduction of motor speed but may be substantially increased over and. above its normal strength and may be in certain cases practically doubled, so that the desired dynamic brake action may be obtained with 'but relatively small current flow in the motor armature.

Figure 1 of the accompanying drawing illustrates my invention as applied to a direct current electric elevator. Figs. 2 and 3 are,wiring.diagrams taken from Fig. l and showing the electrical circuits of the motor in starting and stopping.

Similar parts are represented by like reference characters in all of the figures.

Referring to Fig. 1, an elevator car or other load carrying device C is arranged to be operated by an electric motor M. A manual switch E may be located in the car C and controls a circuit to the reversing switch R. The latter is shown as a throw- ,over switch controlled by electromagnets and normally held in operated osition by gravity. The usual electrical y-released spring-pressed friction-brake is represented by the letter B, while F designates the motor field winding. A resistance G is used in starting the motor and is controlled by an accelerating magnet A. A resistance H is used in slowing down and stopping the 1110- tor and is controlled by astoppiggmagnet S. A main line switch is shown at I.

\Vith this general description, I will now describe, the various parts more in detail, and at the same time point out their operation and the electrical circuits associated therewith.

The first operation is when the lever 1 of the car switch E is brought into electrical engagement with the stationary contact '2 to close a circuit to the solenoid winding 3 of the reversing switch from the and mains. The switch arm 8 is thereby moved in a right hand direction into the position shown with the movable contacts 5, 10 and 12 in electrical engagement with the corresponding stationary conta ts 4, and 11, respectively. This operation establishes the proper armature connections oolrresponding to a right hand movement of the car switch, but'the armature circuit is not as yet closed'on the main line. Assoon as the contacts 4 and 5 come together, a circuit is closed to the operating me at 7 of the main line switch I, which circuit may be traced thro the car switch contacts 4 and 5, wire winding 7, to t e mam. The switch I now raises its core and connected contacts and completes the arma- Cure circuit through the starting resistance G, the motor fiel circuit, and a circuit to the brake. The armature circult may be traced from the main, through the contacts 13 and 14 of switch I, contacts 10 and 9 of the reversing switch, series coil 15, armature brush 16, motor armature brush 17, Contacts 11 and 12, wire 18, contacts 19 and 20 of switch I, starting resistance G, and to the main. The brake circuit is closed across the line at the contacts 13 and 21, and the field circuit is com leted at the contacts 13 and 14. The acce crating magnet A is also connected across the motor armature at the contacts 22 and the reversing switch contacts 9, 10, 11- and 12. The motor-now-starts at slow speed, and as its counterelectro-motive force rises with increasing motor speed, the magnet A will automatically gradually short circuit the starting resistance and permit the motor to run up to full normal speed. The motor circuits at this time are clcarl shown in Fig. 2.

It will be observed that the armature cur rent passes through the series coil 15 of the reversing switch, and since the core of this coil is connected to the switch lever 8, the magnetic pull of the coil 15 is effective materiall to assist the action of gravity in maintaining the switch contacts in firm electrical engagement with the correspondin stationary contacts such as 4, 9 and 11.

n order to stop the motor to bring the car adjacent a floor landing, the operator moves the lever 1 of the car switch to center or off position. This operation immediately cuts off the current supply to the magnets 3 and 7 of the reversing and main line switches, respectively, and the switch 1 opens its upper contacts and establishes its lower contacts. As the switch I drops its contacts, it opencircuits the brake ma met at the contact 21 and establishes a local short circuit containing the resistance H in shunt to the motor armature. This circuit may be traced from the armature brush 16, series coil 15 of the rcversin switch, contacts 9 and 10, resistance H, contacts 23 and 19, wire 18, contacts 12 and 11, to the armature brush 17. The stopping magnet S isnow connected through the contacts 10 and 9 with one armature brush, and through the contacts 24, 13, 23, 19 and 12 to the other brush, hence the stopping magnet will operate according to the varying potential of the motor armature gradually to shortcircuit more or less of the stopping resistance H to cfl'cct a dynamic brake action on the motor, tending to bring it to rest. The brake is not applie immediately its circuit is opened at the contact 21, since a high resistance 25 is connected in parallel with the brake magnet winding which receives the brake magnet discharge and thereby rcvents the instantaneous application oft e brake and in this manner allows sufiicient time for the dynamic brake action to effect a substantial speed reduction before the friction brake is applied.

It will be observed that the current generated by the motor in stopping passes through the series coil 15 of the reversing switch, and this coil will remain energized until the speed of the motor has been substantially reduced. For this reason it becomes absolutely impossible for the operator to effect a too sudden reversal of the motor, since upon reversing the car switch with the motor at speed, the operator may energize the reversing switch solenoid 26 tending to effect a reversal of this switch, but owing to the opposing action of the series coil 15, the power of the coil 26 is not suiiicient to overcome the power of the coil 15 assisted by gravity, until the motor has substantially come to rest. Since the operator cannot effect the reversal of the reversing switch until the motor has practically come to rest, he cannot operate the switch I by reversing the car switch, since the circuit to the operating magnet of the latter will be open at the reversing switch contacts 27 and 5. Therefore the dynamic brake circuit throu h the contacts 23 and 19 of switch I cannot e interfered with unless and until the motor has all but stopped. The motor circuits in stopping are clearly shown in Fig. 3. The operation of the system in a reverse direction is the same as alrcadydescribed and need not be further described, since the circuits for a reverse movement may easily be traced and are similar to those already described.

An important feature of the invention which has not as yet been described, consists in the field circuit of the motor in stopping. This circuit may best be seen by reference to Figs. 2 and 3. In these figures X desi natrs a dynamo or other suitable source 0 electrical energy, which supplies current to the main line and In starting the motor and during running conditions, the motor field F receives current at line potential through the contacts 13 and 14 of the main line switch I. As this switch becomes decnergized to stop the motor and before it establishes its lower contacts, or in other words, is in an intermediate position, the contacts 13 and 14 become separated and the stopping resistance H is connected in series with the motor field across the main line. Since this resistance is very low compared to the ohmic resistance of the field winding,

' the field strength remains substantially constant. As soon however, as the switch I has moved to extreme deenergized position with the contacts 23 and 19 in electrical engagement with each other, the field of the motor receives current at snbstantiallydouble the main line otential. This fact may he seen by following the field circuit in Fig. 3. 6 his circuit may be traced from contact 13, contacts 23 and 19, contacts 12 and 11. armature of motor M, coil 15, contacts 9 and 10, field F, to the line. The motor field, motor M and generator X are therefore connected in series and the field is obviously subjected to a potential which is equal to the arithmetical sum of the potentials of the motor and generator. As the gencrator X assumably operates at constant potent al, and the potential of the motor in stopping is substantially. eual to that of the mam line or generator depending of course on load conditions, it follows that the field excitation is substantially double and this ex- 20; citation is gradually reduced as the motor reduces its speed until the motor finally comes to rest with the field at main line tial and normal strength. From the oregoing it is seen that the field strength i is vast] increased over and above its normal strength during the period of stopping and the dynamic rake current may be reduced to a minimum and still efiect a powbraking action. Since this current ,0 may be substantially less or practically one fault of what it would otherwise have to bc mith a field of normal strendgth, thehcating "ufle'ct is tly reduced an all sparking at b as overcome. 85 ..-'It will-be observed that in changing over thefield'connections, of the motor in stopping, the field circuit is never broken. The connections will always be such that the field will be in circuit with the motor and gener- D aim in series with the ropcr connection as to polarity, so that the old will be subjected to Potential equal to the combined potentillu'ofthe motor and generator and regardlesa jllhether the motor is being driven by 6 .the'load or not.

desirability of having a powerful field'for stopping is well known and heretofore it has been the practice to employ an additional or extra field Winding to effect j) the desired result. While it is of'advantage 'to utilize a series field winding for starling, it is not considered good rractice to Mao-the series field in stopping ue largely to 'the danger of a reverse current in the series field. Hence Where a series field is i1se(l for starting an extra field is added to efi'eet the stopping which means that the motor be supplied with three field windings which introduces complications in the motor and in the controlling system. My invention dots away with the necessity of an extra field while enabling one to use a motor of standard construction hether the same be 9, simple shunt wound motor or a com- 05 pound wound motor.

the main line What I claim and desire to secure by Letters latcnt of the United States is l. The combination with an electric motor, of a reversing switch therefor, a main line s\\'ll(:lt adapted when in one position to close a main line circuit to the motor armature and when in another position to close a local or dynamic brake circuit around the motor armature. and means controlled by lhe current in said local circuit for prevent- 7.: ing the operation of the reversing switch.

2. The combination with an electric motor, of a reversing switch therefor, a main line switch adapted when in one position to close a main line circuit to the motor armature and when in another position to close a local or dynamic brake circuit around the motor armature, and means controlled by the current in said local circuit for holding the reversing switch against movement.

3. The combination with an electric motor, of a reversi switch therefor, a main line switch adap when in one position to close a main line circuit to the motor armature and when in anotherposition to no close a local or dynamic brake circuit around the motor'almatum, and a magnet winding associated with the'rcvcrsing switch and in said local cireuita'dapted to hold the reversing switch against movement wheu'the main line circuit to the motor armature 'is open and the motor is in motion, I l. The combination with a electric motor. of a'main liue'circuit to t n motor armature, aii'dl means for increasing the normal field strength of the motor by applying to the ficldwindinga mtcntial in excess of otcnlia while the motor is rotating andt e main linccircuit to the motor armature 'isbroken. 106

' The combination with an electric motor, of a main line circuit, a switch adapted to connect said circuit to the mortor armature, and circuits controlled by said switch for int-reaming. thenormal potential 110 across the field winding of the motor upon interrupting the main line circuit to the motor armature.

6. The combination with an electric motor; of a main line circuit, and a switch 116 in the said circuit adapted when in one position to connect the main line circuit to the motor armature and when in another position to open the mainline circuit to the armature and to raise the potential across 120 the field winding over and above the main line potential while the armature is rotating.

7. The combination with a shunt wound electric motor, a mainline circuit, and means for imposing a potential higher than the 125 line potential uponthe field by connecting the motor field winding in series with the said main line and armature of the motor in stop ing the motor.

8. 'l e combination with a shunt wound 110 electric motor, a main line, a switch for connecting the motor armature tothe main line and for simultaneously disconnecting said main line and motor armature and connecting the motor field in series with the main line and the motor armature whereby the potential imposed upon the motor field is raised above the potential of the line.

9. The combination with an electric motor, of a main line circuit, and switch mechanism for increasing the potential across the field winding above that of the main line in stop )ing the motor.

10. he combination with a shunt wound electric motor, of a supply circuit, and switch mechanism operative upon stopping the motor for imposing a potential higher than the line potential upon the field by connecting the field of the latter in series with the motor armature and supply. I

11. A shunt wound electric motor, a constant potential source of supply therefor, and means for raising the motor field excitation above that due to the said source of supply .upoit stopping the motor.

- 12. An electric motor having a shunt field, a main line circuit, and means for connecting said motor armature and motor field in parallel to said main line circuit in starting the motor and for connecting said motor armature and field in series with said main line circuit in stopping the motor. n

13. An electric motor comprising a shunt field winding, a. main line circuit," and means for applying a. potential across said field windin na] to the combined potentials of the mam line and the motor armature.

14. An electric motor comprising a shunt field winding, for applying winding equal to the combined potentials of the main line and the motor armature while the latter is being brou ht to rest.

15. An electric motor a old winding connected in parallel to the motor armature during the normal operation of the motor, and means for imposm a potential higher than the line potentia upon the field by connecting said motor armature and field winding in series when stolpping the motor.

16. 11 electric motor, a eld winding connected in parallel to the-motor armature during the normal operation of the motor,

and means for imposing a potential higher a main line circuit, and meansa potential across said field than the line otential upon the field by connecting said motor armature and field winding in series with each other and in selies with a source of current supply.

17 A shunt wound electric motor, a source of supply and means for imposing a potential higher than the line potential upon the field by supplying the motor field with exciting current derived from the said source of supply and the motor armature in series when e motor is-acting as a generator in coming to rest.

18. An electric motor comprising a. field winding, and means for connecting said winding in shunt to the motor armature in starting the motor and for imposing a potential higher than the line otential upon the field by connecting said winding series with the motor armature in stop i i iig the motor.

19. An electric motor prising a field winding, means for com ting said winding in shunt to the motor, armature in starting the motor and in, series with the motor armature and line in stopping the motor, the circuit in said winding remaining unbroken during the ch e over from shunt to series relation with e motor armature. V 20. An electric motor comprising a field windin means for connecting said ing in unt to the motor armature in starting the motor and for connecting said winding in series with the motor armature in sto ping the motor, and a resistance adapted to connected across the motor armature in stopping the motor and controlled. by said means. y

21. An electric motor com winding, a switch adapted or connecting 'windrising a field said winding in shunt to the motor armature when in one position, andfor connecting the said winding in series with the motor armature and line when in another position,

and means for preventing the deenergization of said winding during the movement ofsaid switch.

' In testimony whereof, I have signed my name to this specification in the presence of two subscribing witneses.

WALTER C. STRANGL Witnesses 

